A method for operating a vehicle is known from German Published Patent Application No. 10 2012 211 024, including the specifying of a setpoint power requirement over time for the vehicle on an internal combustion engine, the setpoint power requirement over time being a function of a diagnosis to be carried out on the internal combustion engine; and an accessory being connected to the internal combustion engine when an actual power requirement over time of the vehicle on the internal combustion engine deviates from the setpoint power requirement over time, and the actual power requirement over time of the internal combustion engine is estimated on a route to be driven with the vehicle, and the diagnosis is planned based on a probability that a difference between the actual power requirement over time and the setpoint power requirement over time is able to be compensated for by connecting the accessory to the internal combustion engine, and the diagnosis being prohibited if the probability falls below a predetermined threshold value.